1 /* 2 * Copyright (c) 2001, 2015, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 * 23 */ 24 25 #ifndef SHARE_VM_GC_SHARED_COLLECTEDHEAP_HPP 26 #define SHARE_VM_GC_SHARED_COLLECTEDHEAP_HPP 27 28 #include "gc/shared/gcCause.hpp" 29 #include "gc/shared/gcWhen.hpp" 30 #include "memory/allocation.hpp" 31 #include "runtime/handles.hpp" 32 #include "runtime/perfData.hpp" 33 #include "runtime/safepoint.hpp" 34 #include "utilities/events.hpp" 35 36 // A "CollectedHeap" is an implementation of a java heap for HotSpot. This 37 // is an abstract class: there may be many different kinds of heaps. This 38 // class defines the functions that a heap must implement, and contains 39 // infrastructure common to all heaps. 40 41 class AdaptiveSizePolicy; 42 class BarrierSet; 43 class CollectorPolicy; 44 class GCHeapSummary; 45 class GCTimer; 46 class GCTracer; 47 class MetaspaceSummary; 48 class Thread; 49 class ThreadClosure; 50 class VirtualSpaceSummary; 51 class nmethod; 52 53 class GCMessage : public FormatBuffer<1024> { 54 public: 55 bool is_before; 56 57 public: 58 GCMessage() {} 59 }; 60 61 class GCHeapLog : public EventLogBase<GCMessage> { 62 private: 63 void log_heap(bool before); 64 65 public: 66 GCHeapLog() : EventLogBase<GCMessage>("GC Heap History") {} 67 68 void log_heap_before() { 69 log_heap(true); 70 } 71 void log_heap_after() { 72 log_heap(false); 73 } 74 }; 75 76 // 77 // CollectedHeap 78 // GenCollectedHeap 79 // G1CollectedHeap 80 // ParallelScavengeHeap 81 // 82 class CollectedHeap : public CHeapObj<mtInternal> { 83 friend class VMStructs; 84 friend class IsGCActiveMark; // Block structured external access to _is_gc_active 85 86 private: 87 #ifdef ASSERT 88 static int _fire_out_of_memory_count; 89 #endif 90 91 GCHeapLog* _gc_heap_log; 92 93 // Used in support of ReduceInitialCardMarks; only consulted if COMPILER2 94 // or INCLUDE_JVMCI is being used 95 bool _defer_initial_card_mark; 96 97 MemRegion _reserved; 98 99 protected: 100 BarrierSet* _barrier_set; 101 bool _is_gc_active; 102 103 // Used for filler objects (static, but initialized in ctor). 104 static size_t _filler_array_max_size; 105 106 unsigned int _total_collections; // ... started 107 unsigned int _total_full_collections; // ... started 108 NOT_PRODUCT(volatile size_t _promotion_failure_alot_count;) 109 NOT_PRODUCT(volatile size_t _promotion_failure_alot_gc_number;) 110 111 // Reason for current garbage collection. Should be set to 112 // a value reflecting no collection between collections. 113 GCCause::Cause _gc_cause; 114 GCCause::Cause _gc_lastcause; 115 PerfStringVariable* _perf_gc_cause; 116 PerfStringVariable* _perf_gc_lastcause; 117 118 // Constructor 119 CollectedHeap(); 120 121 // Do common initializations that must follow instance construction, 122 // for example, those needing virtual calls. 123 // This code could perhaps be moved into initialize() but would 124 // be slightly more awkward because we want the latter to be a 125 // pure virtual. 126 void pre_initialize(); 127 128 // Create a new tlab. All TLAB allocations must go through this. 129 virtual HeapWord* allocate_new_tlab(size_t size); 130 131 // Accumulate statistics on all tlabs. 132 virtual void accumulate_statistics_all_tlabs(); 133 134 // Reinitialize tlabs before resuming mutators. 135 virtual void resize_all_tlabs(); 136 137 // Allocate from the current thread's TLAB, with broken-out slow path. 138 inline static HeapWord* allocate_from_tlab(KlassHandle klass, Thread* thread, size_t size); 139 static HeapWord* allocate_from_tlab_slow(KlassHandle klass, Thread* thread, size_t size); 140 141 // Allocate an uninitialized block of the given size, or returns NULL if 142 // this is impossible. 143 inline static HeapWord* common_mem_allocate_noinit(KlassHandle klass, size_t size, TRAPS); 144 145 // Like allocate_init, but the block returned by a successful allocation 146 // is guaranteed initialized to zeros. 147 inline static HeapWord* common_mem_allocate_init(KlassHandle klass, size_t size, TRAPS); 148 149 // Helper functions for (VM) allocation. 150 inline static void post_allocation_setup_common(KlassHandle klass, HeapWord* obj); 151 inline static void post_allocation_setup_no_klass_install(KlassHandle klass, 152 HeapWord* objPtr); 153 154 inline static void post_allocation_setup_obj(KlassHandle klass, HeapWord* obj, int size); 155 156 inline static void post_allocation_setup_array(KlassHandle klass, 157 HeapWord* obj, int length); 158 159 // Clears an allocated object. 160 inline static void init_obj(HeapWord* obj, size_t size); 161 162 // Filler object utilities. 163 static inline size_t filler_array_hdr_size(); 164 static inline size_t filler_array_min_size(); 165 166 DEBUG_ONLY(static void fill_args_check(HeapWord* start, size_t words);) 167 DEBUG_ONLY(static void zap_filler_array(HeapWord* start, size_t words, bool zap = true);) 168 169 // Fill with a single array; caller must ensure filler_array_min_size() <= 170 // words <= filler_array_max_size(). 171 static inline void fill_with_array(HeapWord* start, size_t words, bool zap = true); 172 173 // Fill with a single object (either an int array or a java.lang.Object). 174 static inline void fill_with_object_impl(HeapWord* start, size_t words, bool zap = true); 175 176 virtual void trace_heap(GCWhen::Type when, const GCTracer* tracer); 177 178 // Verification functions 179 virtual void check_for_bad_heap_word_value(HeapWord* addr, size_t size) 180 PRODUCT_RETURN; 181 virtual void check_for_non_bad_heap_word_value(HeapWord* addr, size_t size) 182 PRODUCT_RETURN; 183 debug_only(static void check_for_valid_allocation_state();) 184 185 public: 186 enum Name { 187 GenCollectedHeap, 188 ParallelScavengeHeap, 189 G1CollectedHeap 190 }; 191 192 static inline size_t filler_array_max_size() { 193 return _filler_array_max_size; 194 } 195 196 virtual Name kind() const = 0; 197 198 /** 199 * Returns JNI error code JNI_ENOMEM if memory could not be allocated, 200 * and JNI_OK on success. 201 */ 202 virtual jint initialize() = 0; 203 204 // In many heaps, there will be a need to perform some initialization activities 205 // after the Universe is fully formed, but before general heap allocation is allowed. 206 // This is the correct place to place such initialization methods. 207 virtual void post_initialize(); 208 209 // Stop any onging concurrent work and prepare for exit. 210 virtual void stop() {} 211 212 void initialize_reserved_region(HeapWord *start, HeapWord *end); 213 MemRegion reserved_region() const { return _reserved; } 214 address base() const { return (address)reserved_region().start(); } 215 216 virtual size_t capacity() const = 0; 217 virtual size_t used() const = 0; 218 219 // Return "true" if the part of the heap that allocates Java 220 // objects has reached the maximal committed limit that it can 221 // reach, without a garbage collection. 222 virtual bool is_maximal_no_gc() const = 0; 223 224 // Support for java.lang.Runtime.maxMemory(): return the maximum amount of 225 // memory that the vm could make available for storing 'normal' java objects. 226 // This is based on the reserved address space, but should not include space 227 // that the vm uses internally for bookkeeping or temporary storage 228 // (e.g., in the case of the young gen, one of the survivor 229 // spaces). 230 virtual size_t max_capacity() const = 0; 231 232 // Returns "TRUE" if "p" points into the reserved area of the heap. 233 bool is_in_reserved(const void* p) const { 234 return _reserved.contains(p); 235 } 236 237 bool is_in_reserved_or_null(const void* p) const { 238 return p == NULL || is_in_reserved(p); 239 } 240 241 // Returns "TRUE" iff "p" points into the committed areas of the heap. 242 // This method can be expensive so avoid using it in performance critical 243 // code. 244 virtual bool is_in(const void* p) const = 0; 245 246 DEBUG_ONLY(bool is_in_or_null(const void* p) const { return p == NULL || is_in(p); }) 247 248 // Let's define some terms: a "closed" subset of a heap is one that 249 // 250 // 1) contains all currently-allocated objects, and 251 // 252 // 2) is closed under reference: no object in the closed subset 253 // references one outside the closed subset. 254 // 255 // Membership in a heap's closed subset is useful for assertions. 256 // Clearly, the entire heap is a closed subset, so the default 257 // implementation is to use "is_in_reserved". But this may not be too 258 // liberal to perform useful checking. Also, the "is_in" predicate 259 // defines a closed subset, but may be too expensive, since "is_in" 260 // verifies that its argument points to an object head. The 261 // "closed_subset" method allows a heap to define an intermediate 262 // predicate, allowing more precise checking than "is_in_reserved" at 263 // lower cost than "is_in." 264 265 // One important case is a heap composed of disjoint contiguous spaces, 266 // such as the Garbage-First collector. Such heaps have a convenient 267 // closed subset consisting of the allocated portions of those 268 // contiguous spaces. 269 270 // Return "TRUE" iff the given pointer points into the heap's defined 271 // closed subset (which defaults to the entire heap). 272 virtual bool is_in_closed_subset(const void* p) const { 273 return is_in_reserved(p); 274 } 275 276 bool is_in_closed_subset_or_null(const void* p) const { 277 return p == NULL || is_in_closed_subset(p); 278 } 279 280 // An object is scavengable if its location may move during a scavenge. 281 // (A scavenge is a GC which is not a full GC.) 282 virtual bool is_scavengable(const void *p) = 0; 283 284 void set_gc_cause(GCCause::Cause v) { 285 if (UsePerfData) { 286 _gc_lastcause = _gc_cause; 287 _perf_gc_lastcause->set_value(GCCause::to_string(_gc_lastcause)); 288 _perf_gc_cause->set_value(GCCause::to_string(v)); 289 } 290 _gc_cause = v; 291 } 292 GCCause::Cause gc_cause() { return _gc_cause; } 293 294 // General obj/array allocation facilities. 295 inline static oop obj_allocate(KlassHandle klass, int size, TRAPS); 296 inline static oop array_allocate(KlassHandle klass, int size, int length, TRAPS); 297 inline static oop array_allocate_nozero(KlassHandle klass, int size, int length, TRAPS); 298 299 inline static void post_allocation_install_obj_klass(KlassHandle klass, 300 oop obj); 301 302 // Raw memory allocation facilities 303 // The obj and array allocate methods are covers for these methods. 304 // mem_allocate() should never be 305 // called to allocate TLABs, only individual objects. 306 virtual HeapWord* mem_allocate(size_t size, 307 bool* gc_overhead_limit_was_exceeded) = 0; 308 309 // Utilities for turning raw memory into filler objects. 310 // 311 // min_fill_size() is the smallest region that can be filled. 312 // fill_with_objects() can fill arbitrary-sized regions of the heap using 313 // multiple objects. fill_with_object() is for regions known to be smaller 314 // than the largest array of integers; it uses a single object to fill the 315 // region and has slightly less overhead. 316 static size_t min_fill_size() { 317 return size_t(align_object_size(oopDesc::header_size())); 318 } 319 320 static void fill_with_objects(HeapWord* start, size_t words, bool zap = true); 321 322 static void fill_with_object(HeapWord* start, size_t words, bool zap = true); 323 static void fill_with_object(MemRegion region, bool zap = true) { 324 fill_with_object(region.start(), region.word_size(), zap); 325 } 326 static void fill_with_object(HeapWord* start, HeapWord* end, bool zap = true) { 327 fill_with_object(start, pointer_delta(end, start), zap); 328 } 329 330 // Return the address "addr" aligned by "alignment_in_bytes" if such 331 // an address is below "end". Return NULL otherwise. 332 inline static HeapWord* align_allocation_or_fail(HeapWord* addr, 333 HeapWord* end, 334 unsigned short alignment_in_bytes); 335 336 // Some heaps may offer a contiguous region for shared non-blocking 337 // allocation, via inlined code (by exporting the address of the top and 338 // end fields defining the extent of the contiguous allocation region.) 339 340 // This function returns "true" iff the heap supports this kind of 341 // allocation. (Default is "no".) 342 virtual bool supports_inline_contig_alloc() const { 343 return false; 344 } 345 // These functions return the addresses of the fields that define the 346 // boundaries of the contiguous allocation area. (These fields should be 347 // physically near to one another.) 348 virtual HeapWord** top_addr() const { 349 guarantee(false, "inline contiguous allocation not supported"); 350 return NULL; 351 } 352 virtual HeapWord** end_addr() const { 353 guarantee(false, "inline contiguous allocation not supported"); 354 return NULL; 355 } 356 357 // Some heaps may be in an unparseable state at certain times between 358 // collections. This may be necessary for efficient implementation of 359 // certain allocation-related activities. Calling this function before 360 // attempting to parse a heap ensures that the heap is in a parsable 361 // state (provided other concurrent activity does not introduce 362 // unparsability). It is normally expected, therefore, that this 363 // method is invoked with the world stopped. 364 // NOTE: if you override this method, make sure you call 365 // super::ensure_parsability so that the non-generational 366 // part of the work gets done. See implementation of 367 // CollectedHeap::ensure_parsability and, for instance, 368 // that of GenCollectedHeap::ensure_parsability(). 369 // The argument "retire_tlabs" controls whether existing TLABs 370 // are merely filled or also retired, thus preventing further 371 // allocation from them and necessitating allocation of new TLABs. 372 virtual void ensure_parsability(bool retire_tlabs); 373 374 // Section on thread-local allocation buffers (TLABs) 375 // If the heap supports thread-local allocation buffers, it should override 376 // the following methods: 377 // Returns "true" iff the heap supports thread-local allocation buffers. 378 // The default is "no". 379 virtual bool supports_tlab_allocation() const = 0; 380 381 // The amount of space available for thread-local allocation buffers. 382 virtual size_t tlab_capacity(Thread *thr) const = 0; 383 384 // The amount of used space for thread-local allocation buffers for the given thread. 385 virtual size_t tlab_used(Thread *thr) const = 0; 386 387 virtual size_t max_tlab_size() const; 388 389 // An estimate of the maximum allocation that could be performed 390 // for thread-local allocation buffers without triggering any 391 // collection or expansion activity. 392 virtual size_t unsafe_max_tlab_alloc(Thread *thr) const { 393 guarantee(false, "thread-local allocation buffers not supported"); 394 return 0; 395 } 396 397 // Can a compiler initialize a new object without store barriers? 398 // This permission only extends from the creation of a new object 399 // via a TLAB up to the first subsequent safepoint. If such permission 400 // is granted for this heap type, the compiler promises to call 401 // defer_store_barrier() below on any slow path allocation of 402 // a new object for which such initializing store barriers will 403 // have been elided. 404 virtual bool can_elide_tlab_store_barriers() const = 0; 405 406 // If a compiler is eliding store barriers for TLAB-allocated objects, 407 // there is probably a corresponding slow path which can produce 408 // an object allocated anywhere. The compiler's runtime support 409 // promises to call this function on such a slow-path-allocated 410 // object before performing initializations that have elided 411 // store barriers. Returns new_obj, or maybe a safer copy thereof. 412 virtual oop new_store_pre_barrier(JavaThread* thread, oop new_obj); 413 414 // Answers whether an initializing store to a new object currently 415 // allocated at the given address doesn't need a store 416 // barrier. Returns "true" if it doesn't need an initializing 417 // store barrier; answers "false" if it does. 418 virtual bool can_elide_initializing_store_barrier(oop new_obj) = 0; 419 420 // If a compiler is eliding store barriers for TLAB-allocated objects, 421 // we will be informed of a slow-path allocation by a call 422 // to new_store_pre_barrier() above. Such a call precedes the 423 // initialization of the object itself, and no post-store-barriers will 424 // be issued. Some heap types require that the barrier strictly follows 425 // the initializing stores. (This is currently implemented by deferring the 426 // barrier until the next slow-path allocation or gc-related safepoint.) 427 // This interface answers whether a particular heap type needs the card 428 // mark to be thus strictly sequenced after the stores. 429 virtual bool card_mark_must_follow_store() const = 0; 430 431 // If the CollectedHeap was asked to defer a store barrier above, 432 // this informs it to flush such a deferred store barrier to the 433 // remembered set. 434 virtual void flush_deferred_store_barrier(JavaThread* thread); 435 436 // Perform a collection of the heap; intended for use in implementing 437 // "System.gc". This probably implies as full a collection as the 438 // "CollectedHeap" supports. 439 virtual void collect(GCCause::Cause cause) = 0; 440 441 // Perform a full collection 442 virtual void do_full_collection(bool clear_all_soft_refs) = 0; 443 444 // This interface assumes that it's being called by the 445 // vm thread. It collects the heap assuming that the 446 // heap lock is already held and that we are executing in 447 // the context of the vm thread. 448 virtual void collect_as_vm_thread(GCCause::Cause cause); 449 450 // Returns the barrier set for this heap 451 BarrierSet* barrier_set() { return _barrier_set; } 452 void set_barrier_set(BarrierSet* barrier_set); 453 454 // Returns "true" iff there is a stop-world GC in progress. (I assume 455 // that it should answer "false" for the concurrent part of a concurrent 456 // collector -- dld). 457 bool is_gc_active() const { return _is_gc_active; } 458 459 // Total number of GC collections (started) 460 unsigned int total_collections() const { return _total_collections; } 461 unsigned int total_full_collections() const { return _total_full_collections;} 462 463 // Increment total number of GC collections (started) 464 // Should be protected but used by PSMarkSweep - cleanup for 1.4.2 465 void increment_total_collections(bool full = false) { 466 _total_collections++; 467 if (full) { 468 increment_total_full_collections(); 469 } 470 } 471 472 void increment_total_full_collections() { _total_full_collections++; } 473 474 // Return the AdaptiveSizePolicy for the heap. 475 virtual AdaptiveSizePolicy* size_policy() = 0; 476 477 // Return the CollectorPolicy for the heap 478 virtual CollectorPolicy* collector_policy() const = 0; 479 480 // Iterate over all objects, calling "cl.do_object" on each. 481 virtual void object_iterate(ObjectClosure* cl) = 0; 482 483 // Similar to object_iterate() except iterates only 484 // over live objects. 485 virtual void safe_object_iterate(ObjectClosure* cl) = 0; 486 487 // NOTE! There is no requirement that a collector implement these 488 // functions. 489 // 490 // A CollectedHeap is divided into a dense sequence of "blocks"; that is, 491 // each address in the (reserved) heap is a member of exactly 492 // one block. The defining characteristic of a block is that it is 493 // possible to find its size, and thus to progress forward to the next 494 // block. (Blocks may be of different sizes.) Thus, blocks may 495 // represent Java objects, or they might be free blocks in a 496 // free-list-based heap (or subheap), as long as the two kinds are 497 // distinguishable and the size of each is determinable. 498 499 // Returns the address of the start of the "block" that contains the 500 // address "addr". We say "blocks" instead of "object" since some heaps 501 // may not pack objects densely; a chunk may either be an object or a 502 // non-object. 503 virtual HeapWord* block_start(const void* addr) const = 0; 504 505 // Requires "addr" to be the start of a chunk, and returns its size. 506 // "addr + size" is required to be the start of a new chunk, or the end 507 // of the active area of the heap. 508 virtual size_t block_size(const HeapWord* addr) const = 0; 509 510 // Requires "addr" to be the start of a block, and returns "TRUE" iff 511 // the block is an object. 512 virtual bool block_is_obj(const HeapWord* addr) const = 0; 513 514 // Returns the longest time (in ms) that has elapsed since the last 515 // time that any part of the heap was examined by a garbage collection. 516 virtual jlong millis_since_last_gc() = 0; 517 518 // Perform any cleanup actions necessary before allowing a verification. 519 virtual void prepare_for_verify() = 0; 520 521 // Generate any dumps preceding or following a full gc 522 void pre_full_gc_dump(GCTimer* timer); 523 void post_full_gc_dump(GCTimer* timer); 524 525 VirtualSpaceSummary create_heap_space_summary(); 526 GCHeapSummary create_heap_summary(); 527 528 MetaspaceSummary create_metaspace_summary(); 529 530 // Print heap information on the given outputStream. 531 virtual void print_on(outputStream* st) const = 0; 532 // The default behavior is to call print_on() on tty. 533 virtual void print() const { 534 print_on(tty); 535 } 536 // Print more detailed heap information on the given 537 // outputStream. The default behavior is to call print_on(). It is 538 // up to each subclass to override it and add any additional output 539 // it needs. 540 virtual void print_extended_on(outputStream* st) const { 541 print_on(st); 542 } 543 544 virtual void print_on_error(outputStream* st) const; 545 546 // Print all GC threads (other than the VM thread) 547 // used by this heap. 548 virtual void print_gc_threads_on(outputStream* st) const = 0; 549 // The default behavior is to call print_gc_threads_on() on tty. 550 void print_gc_threads() { 551 print_gc_threads_on(tty); 552 } 553 // Iterator for all GC threads (other than VM thread) 554 virtual void gc_threads_do(ThreadClosure* tc) const = 0; 555 556 // Print any relevant tracing info that flags imply. 557 // Default implementation does nothing. 558 virtual void print_tracing_info() const = 0; 559 560 void print_heap_before_gc(); 561 void print_heap_after_gc(); 562 563 // Registering and unregistering an nmethod (compiled code) with the heap. 564 // Override with specific mechanism for each specialized heap type. 565 virtual void register_nmethod(nmethod* nm); 566 virtual void unregister_nmethod(nmethod* nm); 567 568 void trace_heap_before_gc(const GCTracer* gc_tracer); 569 void trace_heap_after_gc(const GCTracer* gc_tracer); 570 571 // Heap verification 572 virtual void verify(bool silent, VerifyOption option) = 0; 573 574 // Non product verification and debugging. 575 #ifndef PRODUCT 576 // Support for PromotionFailureALot. Return true if it's time to cause a 577 // promotion failure. The no-argument version uses 578 // this->_promotion_failure_alot_count as the counter. 579 inline bool promotion_should_fail(volatile size_t* count); 580 inline bool promotion_should_fail(); 581 582 // Reset the PromotionFailureALot counters. Should be called at the end of a 583 // GC in which promotion failure occurred. 584 inline void reset_promotion_should_fail(volatile size_t* count); 585 inline void reset_promotion_should_fail(); 586 #endif // #ifndef PRODUCT 587 588 #ifdef ASSERT 589 static int fired_fake_oom() { 590 return (CIFireOOMAt > 1 && _fire_out_of_memory_count >= CIFireOOMAt); 591 } 592 #endif 593 594 public: 595 // Copy the current allocation context statistics for the specified contexts. 596 // For each context in contexts, set the corresponding entries in the totals 597 // and accuracy arrays to the current values held by the statistics. Each 598 // array should be of length len. 599 // Returns true if there are more stats available. 600 virtual bool copy_allocation_context_stats(const jint* contexts, 601 jlong* totals, 602 jbyte* accuracy, 603 jint len) { 604 return false; 605 } 606 607 /////////////// Unit tests /////////////// 608 609 NOT_PRODUCT(static void test_is_in();) 610 }; 611 612 // Class to set and reset the GC cause for a CollectedHeap. 613 614 class GCCauseSetter : StackObj { 615 CollectedHeap* _heap; 616 GCCause::Cause _previous_cause; 617 public: 618 GCCauseSetter(CollectedHeap* heap, GCCause::Cause cause) { 619 assert(SafepointSynchronize::is_at_safepoint(), 620 "This method manipulates heap state without locking"); 621 _heap = heap; 622 _previous_cause = _heap->gc_cause(); 623 _heap->set_gc_cause(cause); 624 } 625 626 ~GCCauseSetter() { 627 assert(SafepointSynchronize::is_at_safepoint(), 628 "This method manipulates heap state without locking"); 629 _heap->set_gc_cause(_previous_cause); 630 } 631 }; 632 633 #endif // SHARE_VM_GC_SHARED_COLLECTEDHEAP_HPP